The organization of the projection from the cerebral cortex to the striatum in the rat

The nucleus accumbens and learning and memory

Recent research on the nucleus accumbens (NA) indicates that this brain region is involved in learning and memory processes in a way that is separable from its other well-known roles in behavior, such as motivation, reward, and locomotor activity. These findings have suggested that 1) the NA may be involved in declarative, or hippocampal formation-dependent learning and memory, and not in several other non-declarative forms of learning and memory, and 2) the NA may be selectively involved in certain stages of learning and memory. These characteristics suggest that the NA may be part of a larger striatal system which subserves acquisition and consolidation, but is not a site of long-term storage, of different forms of learning and memory.

Evidence of apoptotic procedure in deafferented striatum after cortical injury in young adult rats

In denervated striatum after excitotoxic cortical lesion in young adult rats, apoptotic cells, though quite few, were observed by TUNEL 2 weeks after surgery. Also, prominent expressions of p53 were observed at the same time. These data indicate that apoptotic procedure may be involved in the denervation-induced degeneration even in young adults.

Cortical input to the basal forebrain

The arborization pattern and postsynaptic targets of corticofugal axons in basal forebrain areas have been studied by the combination of anatomical tract-tracing and pre- and postembedding immunocytochemistry. The anterograde neuronal tracer Phaseolus vulgaris leucoagglutinin was iontophoretically delivered into different neocortical (frontal, parietal, occipital), allocortical (piriform) and mesocortical (insular, prefrontal) areas in rats. To identify the transmitter phenotype in pre- or postsynaptic elements, the tracer staining was combined with immunolabeling for either glutamate or GABA, or with immunolabeling for choline acetyltransferase or parvalbumin. Tracer injections into medial and ventral prefrontal areas gave rise to dense terminal arborizations in extended basal forebrain areas, particularly in the horizontal limb of the diagonal band and the region ventral to it. Terminals were also found to a lesser extent in the ventral part of the substantia innominata and in ventral pallidal areas adjoining ventral striatal territories. Similarly, labeled fibers from the piriform and insular cortices were found to reach lateral and ventral parts of the substantia innominata, where terminal varicosities were evident. In contrast, descending fibers from neocortical areas were smooth, devoid of terminal varicosities, and restricted to the myelinated fascicles of the internal capsule en route to more caudal targets. Ultrastructural studies obtained indicated that corticofugal axon terminals in the basal forebrain areas form synaptic contact primarily with dendritic spines or small dendritic branches (89%); the remaining axon terminals established synapses with dendritic shafts. All tracer labeled axon terminals were immunonegative for GABA, and in the cases investigated, were found to contain glutamate immunoreactivity. In material stained for the anterograde tracer and choline acetyltransferase, a total of 63 Phaseolus vulgaris leucoagglutinin varicosities closely associated with cholinergic profiles were selected for electron microscopic analysis. From this material, 37 varicosities were identified as establishing asymmetric synaptic contacts with neurons that were immunonegative for choline acetyltransferase, including spines and small dendrites (87%) or dendritic shafts (13%). Unequivocal evidence for synaptic interactions between tracer labeled terminals and cholinergic profiles could not be obtained in the remaining cases. From material stained for the anterograde tracer and parvalbumin, 40% of the labeled terminals investigated were found to establish synapses with parvalbumin-positive elements; these contacts were on dendritic shafts and were of the asymmetrical type. The present data suggest that corticofugal axons innervate forebrain neurons that are primarily inhibitory and non-cholinergic; local forebrain axonal arborizations of these cells may represent a mechanism by which prefrontal cortical areas control basal forebrain cholinergic neurons outside the traditional boundaries of pallidal areas.

Cellular mechanisms underlying reinforcement-related processing in the nucleus accumbens: electrophysiological studies in behaving animals

Numerous investigations have implicated the nucleus accumbens (NA) as an important neural substrate involved in mediating reinforcement-related processing. Electrophysiological studies in behaving animals enable a direct examination of cellular mechanisms underlying this process via characterization of NA activity at critical times during responding for food, water, or drug reward. Electrophysiological studies are reported that examined the activity of NA neurons during water- and cocaine-reinforced responding in rats. These studies reveal that some NA neurons exhibit changes (increases or decreases) in firing rate synchronized to the response-contingent delivery of water or cocaine. Furthermore, the sampled population of NA neurons exhibited less synchronized cell firing during the response for cocaine than for the water reward. NA activity during cocaine self-administration was explicitly coupled to the behavioral state of the animal and was markedly influenced by the stimulus context in which the drug was delivered. These findings are discussed with respect to the dynamic properties of NA activity and its importance as an underlying cellular substrate mediating reinforcement-related events in the behaving animal.

Sensitization of the striatal dopaminergic system induced by chronic administration of a glutamate antagonist in the rat

The aim of the present study was to assess in the rat the pharmacological, biochemical and molecular (including in situ hybridization) consequences in the striatum of a prolonged (50 days) treatment with dizocilpine maleate (MK-801), an N-methyl-D-aspartate (NMDA) antagonist. We observed a sensitization-like effect characterized by a behavioural hyperresponsiveness to an acute injection of haloperidol (0.25 mg/kg), a dopaminergic antagonist. In rats chronically treated with MK-801, this hyperresponsiveness was associated with an increased D2 receptor (D2R) density in the striatum. At the transcriptional level, the D2R mRNA was also enhanced in the striatum. Quantitative in situ hybridization studies revealed that the number of neurons expressing the D2R mRNA was significantly enhanced in treated rats, whereas the mean amount of message per cell was unchanged. These changes could represent the neurobiological substrate of the observed sensitization. These results suggest that the D2R gene is under glutamate control via NMDA receptor in striatal neurons.

Subthalamic ablation reverses changes in basal ganglia oxidative metabolism and motor response to apomorphine induced by nigrostriatal lesion in rats

In Parkinson's disease, the functional architecture of the basal ganglia nuclei undergoes profound alterations, one of the most important of which is overactivity of the basal ganglia output nuclei. This phenomenon seems to be intimately related to pathological overactivity of the subthalamic nucleus, which directly modulates the basal ganglia output through its glutamatergic projections. In this study, we investigated the effects of unilateral subthalamic nucleus lesions on the activities of succinate dehydrogenase and cytochrome oxidase, two markers of neuronal activity, in rats with prior unilateral lesions of the nigrostriatal tract. We also explored the effect of subthalamic nucleus lesions on the rotational response to systemic apomorphine. Rats with unilateral lesions of the nigrostriatal tract showed ipsilateral increases in enzyme activity in the basal ganglia output nuclei, entopeduncular nucleus and substantia nigra pars reticulata. Selective subthalamic nucleus destruction completely reversed this phenomenon. In addition, subthalamic nucleus lesions abolished the rotational response to apomorphine. These results confirm that overactivity of the subthalamic nucleus plays a pivotal role in the functional alterations of basal ganglia associated with Parkinson's disease. They also shed further light on the neural mechanisms through which manipulations of subthalamic activity can ameliorate Parkinson's disease symptoms.

Transplantation of mesencephalic cell suspension in dopamine-denervated striatum of the rat. II. Effects on corticostriatal transmission

The present study has been designed to investigate whether intrastriatal implantation of mesencephalic dopamine (DA)-synthetizing neurons into the striatum (ST) of rats whose substantia nigra (SN) was previously destroyed by 6-hydroxydopamine (6-OHDA) restores the pattern of corticostriatal transmission from the medial prelimbic and sensorimotor cortices. In 6-month-old normal animals electrical stimulation of these two functionally unrelated cortices evoked a short latency and brief excitation in 81.6% of neurons recorded in the dorsolateral ST. This percentage decreased significantly (70.6%) in age-matched animals whose dopaminergic nigrostriatal pathway was unilaterally destroyed by 6-OHDA 3 months before recording. However a significant increase in neurons (36.9%) which could be simultaneously activated from the two cortices in comparison to intact rats was noted. In addition the lesion caused a significant decrease in the threshold current required to evoke activation of striatal neurons from the sensorimotor cortex. The increase in the number of striatal neurons responding simultaneously to cortical stimulations demonstrates that destruction of the dopaminergic nigrostriatal pathway causes a loss of the focusing action of DA on corticostriatal transmission. Transplantation of embryonic mesencephalic neurons appears to reestablish this action since the number of convergent responses was significantly decreased in grafted animals (23.5%) in comparison to denervated (36.9%) and sham-grafted (35.1%) animals. Furthermore, the grafts showed a trend to increase current intensities required to evoke activation of striatal cells from both cortices. The action of grafted mesencephalic neurons over prelimbic and sensorimotor cortical inputs to the dorsal ST could be involved in recovery of grafted animals in the correct execution of complex sensorimotor tasks requiring integration of different cortical signals within the ST.

The range and distribution of murine central nervous system cells infected with the gamma(1)34.5- mutant of herpes simplex virus 1

Wild-type herpes simplex virus 1 (HSV-1) multiplies, spreads, and rapidly destroys cells of the murine central nervous system (CNS). In contrast, mutants lacking both copies of the gamma(1)34.5- gene have been shown to be virtually lacking in virulence even after direct inoculation of high-titered virus into the CNS of susceptible mice (J. Chou, E. R. Kern, R. J. Whitley, and B. Roizman, Science 250:1262-1266, 1990). To investigate the host range and distribution of infected cells in the CNS of mice, 4- to 5-week-old mice were inoculated stereotaxically into the caudate/putamen with 3 x 10(5) PFU of the gamma(1)34.5- virus R3616. Four-micrometer-thick sections of mouse brains removed on day 3, 5, or 7 after infection were reacted with a polyclonal antibody directed primarily to structural proteins of the virus and with antibodies specific for neurons, astrocytes, or oligodendrocytes. This report shows the following: (i) most of the tissue damage caused by R3616 was at the site of injection, (ii) the virus spread by retrograde transport from the site of infection to neuronal cell nuclei at distant sites and to ependymal cells by cerebrospinal fluid, (iii) the virus infected neurons, astrocytes, oligodendrocytes, and ependymal cells and hence did not discriminate among CNS cells, (iv) viral replication in some neurons could be deduced from the observation of infected astrocytes and oligodendrocytes at distant sites, and (v) infected cells were being efficiently cleared from the nervous system by day 7 after infection. We conclude that the gamma(1)34.5- attenuation phenotype is reflected in a gross reduction in the ability of the virus to replicate and spread from cell to cell and is not due to a restricted host range. The block in viral replication appears to be a late event in viral replication.

Local release of GABAergic inhibition in the motor cortex induces immediate-early gene expression in indirect pathway neurons of the striatum

The neocortex is thought to exert a powerful influence over the functions of the basal ganglia via its projection to the striatum. It is not known, however, whether corticostriatal effects are similar across different types of striatal projection neurons and interneurons or are unique for cells having different functions within striatal networks. To examine this question, we developed a method for focal synchronous activation of the primary motor cortex (MI) of freely moving rats by local release of GABAergic inhibition. With this method, we monitored cortically evoked activation of two immediate-early gene protein products, c-Fos and JunB, in phenotypically identified striatal neurons. We further studied the influence of glutamate receptor antagonists on the stimulated expression of c-Fos, JunB, FosB, and NGFI-A. Local disinhibition of MI elicited remarkably selective induction of c-Fos and JunB in enkephalinergic projection neurons. These indirect pathway neurons, through their projections to the globus pallidus, can inhibit thalamocortical motor circuits. The dynorphin-containing projection neurons of the direct pathway, with opposite effects on the thalamocortical circuits, showed very little induction of c-Fos or JunB. The gene response of striatal interneurons was also highly selective, affecting principally parvalbumin- and NADPH diaphorase-expressing interneurons. The glutamate NMDA receptor antagonist MK-801 strongly reduced the cortically evoked striatal gene expression in all cell types for each gene examined. Because the gene induction that we found followed known corticostriatal somatotopy, was dose-dependent, and was selectively sensitive to glutamate receptor antagonists, we suggest that the differential activation patterns reflect functional specialization of cortical inputs to the direct and indirect pathways of the basal ganglia and functional plasticity within these circuits.

Firing rate dependent effect of cocaine on single neurons of the rat lateral striatum

Cocaine's effects on striatal neurons related to vertical head movement were studied during a task requiring vertical head movement. The proportion of long-distance head movements was increased by low doses but decreased by the high dose, which produced stereotypic head bobbing. At all doses, normally low firing rates related to movement were elevated to a greater degree than were normally high firing rates. At the high dose, normally high firing rates were strongly suppressed, a restriction which may contribute to the decreased behavioral diversity characteristic of stereotypy.

Cortical protection by localized striatal injection of IL-1ra following cerebral ischemia in the rat

Interleukin-1 (IL-1) receptor antagonist (IL-1ra) markedly reduces infarct volume induced by middle cerebral artery occlusion (MCAO) in the rat, when injected either centrally (intracerebroventricularly) or peripherally. The site or sites of action of IL-1 in stroke pathology, however, are not known. The present study investigated the site(s) of action of IL-1/IL-1ra in ischemic brain damage by studying the effects of local injection of IL-1ra into the cortex or striatum following permanent MCAO in the rat. Cortical injection of IL-1ra (5 micrograms) did not affect infarct volume in the cortex or striatum measured 24 h after MCAO. In contrast, striatal injection of IL-1ra ipsilateral to the infarction caused a significant and highly reproducible reduction of cortical (37%, p < 0.001) and striatal damage (27%, p < 0.001, corrected for edema) compared with vehicle-injected animals. Injection of IL-1ra (5 micrograms) into the striatum, contralateral to the infarction, resulted in a small (9%) but significant (p < 0.001) reduction of ipsilateral cortical damage, with no effect on ipsilateral striatal damage. Injection of a higher dose of IL-1ra (7.5 micrograms) in the contralateral striatum caused a further inhibition of ipsilateral cortical damage (24%, p < 0.001) and a significant reduction of ipsilateral striatal damage (16%, p < 0.001). In separate groups of rats, it was established that core temperature (measured continuously in free-moving animals with remote radiotelemetry) was not affected by striatal or cortical injection of IL-1ra. These data show that injection of IL-1ra into the striatum but not the cortex reduces infarct volume in both the striatum and the cortex, independently of effects on core temperature. These results imply that blocking striatal IL-1 contributes to IL-1ra-protective effects. We hypothesize that IL-1 may influence striatal distal cortical damage through either the release of specific substances or activation of polysynaptic pathways.

The projection from the striatum to the nucleus basalis in the rat: an electron microscopic study

Previous studies have shown that the striatum provides synaptic inputs to the globus pallidus and entopeduncular nucleus in which GABA is co-localized with the peptides enkephalin and substance P. The aim of this study in the rat was to determine whether the striatal projections also make synaptic contact with the cholinergic neurons of the nucleus basalis, which lie near to the pallidal areas in the rat brain. The anterograde tracer biocytin was injected into different parts of the striatum, and brain sections were stained for biocytin and choline acetyltransferase immunoreactivity by using a dual colour method. Terminals labelled with biocytin by anterograde transport and which made synaptic contact with choline acetyltransferase-positive soma and dendrites were identified by light-electron microscopic correlation methods. In the cases where the biocytin injections had been made in the dorsal or lateral striatum, biocytin-labelled terminals made synaptic contact with cholinergic cells in the region between the main termination zones in the globus pallidus and the entopeduncular nucleus. In the cases where the injections had been made in the ventromedial and posterior striatum, there was greater overlap between choline acetyltransferase-positive structures and biocytin-labelled terminals in the main termination zones in the globus pallidus or entopeduncular nucleus, but relatively few of these terminals made synaptic contacts on to the cholinergic neurons. The results therefore indicate that the cholinergic nucleus basalis cells receive a relatively sparse synaptic input from all parts of the striatum. It has recently been shown that the cholinergic cells of the nucleus basalis selectively express high levels of substance P and opioid receptor messenger RNAs, while the non-cholinergic pallidal cells have much higher levels of GABA(A) receptor subunit messenger RNAs. It is concluded that the cholinergic neurons of the nucleus basalis in the rat may be selectively responsive to the peptidergic components of the striatal outputs, and that they are most likely to be influenced by both the limbic and sensorimotor parts of the striatum.

Comparison of the effects of an ampakine with those of methamphetamine on aggregate neuronal activity in cortex versus striatum

The present study used in situ hybridization to c-fos mRNA to compare the effects of an 'ampakine' (a positive modulator of AMPA type glutamate receptors) with those of methamphetamine on the balance of aggregate neuronal activity in the cortex versus striatum. Methamphetamine (n = 11) induced a marked increase in c-fos mRNA in the dorsomedial quadrant of the striatum and a 21% smaller, but still reliable, increase in the ventrolateral quadrant. The drug also elevated c-fos mRNA levels in the ventral and medial segments of the orbitofrontal cortex but had no detectable effects in motor and somatosensory neocortices. The ampakine (n = 11) caused a near inverse pattern of changes; i.e. a sizable increase in somatosensory labeling and a significant decrease in striatal labeling with statistically insignificant effects in motor and orbitofrontal cortex. Within-rat cortical and striatal values were correlated in both the vehicle (n = 11) and ampakine groups, and appropriate comparisons established that the ampakine caused 27-55% increases in the ratio of cortical to striatal labeling. These results are in accord with the idea that facilitation of glutamatergic transmission has 'network level' effects that are opposite in nature to those resulting from enhanced dopaminergic transmission. The potential relevance of ampakines alone or in conjunction with dopamine antagonists for the treatment of schizophrenia is discussed.

Distributions of single neurons related to body parts in the lateral striatum of the rat

Single unit recordings in awake, unrestrained rats confirmed and extended previous findings regarding the functional organization of the lateral striatum. In individual electrode tracks, clusters of neurons related functionally to an individual body part were interspersed with clusters related to other body parts. The overlapping distributions of these neurons were arranged somatotopically in the dorsal-ventral dimension. The distribution of hind limb neurons was most dorsal and showed no overlap with the distribution of neurons related to oral sensorimotor activity. Oral representation was most ventral of all body parts and extended to the ventral boundary of the lateral striatum. Representations of other body parts overlapped with that of the hind limb dorsally but differed primarily in the degree to which they extended ventrally. Forelimb representation extended farther ventrally than that of the hind limb, but did not extend as far ventrally as that of the neck. Despite substantial overlap in the dorsal-to-ventral order of hind limb-forelimb-neck-face representations, single neurons showed no evidence of overlap, or convergence, of body parts. These data provide a more complete description of the dorsal-ventral somatotopy in the lateral striatum of the rat, which as shown previously, extends throughout the medial-lateral, and much of the anterior-posterior dimensions of the lateral striatum.

Behavioral functions of nucleus accumbens dopamine: empirical and conceptual problems with the anhedonia hypothesis

Nucleus accumbens (DA) has been implicated in a number of different behavioral functions, but most commonly it is said to be involved in "reward" or "reinforcement". In the present article, the putative reinforcement functions of accumbens DA are summarized in a manner described as the "General Anhedonia Model". According to this model, the DA innervation of the nucleus accumbens is conceived of as a crucial link in the "reward system", which evolved to mediate the reinforcing effects of natural stimuli such as food. The reward system is said to be activated by natural reinforcing stimuli, and this activation mediates the reinforcing effects of these natural stimuli. According to this view, other stimuli such as brain stimulation and drugs can activate this system, which leads to these stimuli being reinforcing as well. Interference with DA systems is said to blunt the reinforcing effects of these rewarding stimuli, leading to "extinction". This general model of the behavioral functions of accumbens DA is utilized widely as a theoretical framework for integrating research findings. Nevertheless, there are several difficulties with the General Anhedonia Model. Several studies have observed substantial differences between the effects of extinction and the effects of DA antagonism or accumbens DA depletions. Studies involving aversive conditions indicate that DA antagonists and accumbens DA depletions can interfere with avoidance behavior, and also have demonstrated that accumbens DA release is increased by stressful or aversive stimuli. Although accumbens DA is important for drug abuse phenomena, particularly stimulant self-administration, studies that involve other reinforcers are more problematic. A large body of evidence indicates that low doses of dopamine antagonists, or depletions of accumbens DA, do not impair fundamental aspects of food motivation such as chow consumption and simple instrumental responses for food. This is particularly important, in view of the fact that many behavioral researchers consider the regulation of food motivation to be a fundamental aspect of food reinforcement. Finally, studies employing cost/benefit analyses are reviewed, and in these studies considerable evidence indicates that accumbens DA is involved in the allocation of responses in relation to various reinforcers. Nucleus accumbens DA participates in the function of enabling organisms to overcome response costs, or obstacles, in order to obtain access to stimuli such as food. In summary, nucleus accumbens DA is not seen as directly mediating food reinforcement, but instead is seen as a higher order sensorimotor integrator that is involved in modulating response output in relation to motivational factors and response constraints. Interfering with accumbens DA appears to partially dissociate the process of primary reinforcement from processes regulating instrumental response initiation, maintenance and selection.

Tremulous characteristics of the vacuous jaw movements induced by pilocarpine and ventrolateral striatal dopamine depletions

Vacuous jaw movements induced by the muscarinic agonist pilocarpine and striatal dopamine depletions were examined using a slow motion videotape system. With this procedure, rats were videotaped in a Plexiglas tube so that the profile of the head region could be seen. Vacuous jaw movements were analyzed by examining the tape at 1/6 normal speed. An observer recorded each jaw movement using a computer, and the computer program re-calculated the temporal characteristics of jaw movement responses back to normal speed. The interresponse time was recorded for each jaw movement, and each jaw movement interresponse time was assigned to a 50 ms wide time bin. Thus, the distribution of interresponse times could be used to analyze the temporal characteristics of jaw movement responses. In the first experiment, rats were administered saline vehicle, 1.0 mg/kg and 2.0 mg/kg pilocarpine. The rats were videotaped 10-15 min after injection, and the data were analyzed as described above. Pilocarpine induced very high levels of vacuous jaw movements, and the vast majority of all movements occurred in "bursts" with interresponse times of 1.0 s or less. Analysis of the interresponse time distributions showed that most of the jaw movements were within the 150-350 ms range. The modal jaw movement interresponse time was in the 150-200 ms range, which corresponds to a local frequency of 5-6.66 Hz. In the second experiment, the neurotoxic agent 6-hydroxydopamine was injected directly into the ventrolateral striatum in order to produce a local dopamine depletion. The dopamine-depleted rats were observed for jaw movements 7 days after surgery. The overall level of jaw movement activity resulting from dopamine-depletion was much lower than that produced by pilocarpine. There was a significant inverse correlation between ventrolateral striatal dopamine levels and total number of vacuous jaw movements. Videotape analysis indicated that the temporal characteristics of jaw movements induced by dopamine depletions were similar to those shown with pilocarpine. These experiments indicate that vacuous jaw movements induced by pilocarpine and striatal dopamine depletion occur in a frequency range similar to that shown in parkinsonian tremor.

Sensory and cognitive functions of the basal ganglia

Recent studies have found that the basal ganglia are involved in diverse behavioral activities and suggest that they have executive functions. Highlights from the past year include anatomical and clinical studies that have used sophisticated, novel methods to confirm a role for the basal ganglia in somatosensory discrimination, visual perception, spatial working memory and habit learning.

The effects of limbic lesions on locomotion and stereotypy elicited by dopamine agonists in the rat

The purpose of this experiment was to investigate the functional contributions of various limbic structures to locomotion and stereotypy induced by dopaminergic drugs. Female rats were randomly assigned to one of 5 groups (n = 10-14 rats/group) that received either a lesion of the hippocampus (colchicine + kainic acid), basolateral amygdala (quinolinic acid), frontal cortex (aspiration), nucleus accumbens (ibotenic acid), or served as unoperated controls. Beginning at least 2 weeks following surgery locomotion (measured as photocell beam breaks) elicited by D-amphetamine (0.0, 0.32, 1.0 and 3.2 mg/kg), SKF 82958 (0.0, 0.04, 0.08 and 0.16 mg/kg) or quinpirole (0.0, 0.25, 0.1 and 0.5 mg/kg) was determined. In agreement with previous results rats with hippocampal lesions were hyperactive in response to amphetamine. In comparison to these changes in drug-induced locomotion, lesions of the basolateral amygdala, and frontal cortex had only minor effects on drug-induced locomotion. Lesions of the nucleus accumbens produced consistent hyperactivity that was suppressed by doses of amphetamine or quinpirole that elicited behavioral stereotypy. These results provide evidence suggesting that, in comparison to other limbic structures that have substantial inputs to the nucleus accumbens, the hippocampus play a relatively prominent role in the modulation of drug-induced locomotion.

The effect of neocortical lesions on the number of cells in neonatal or adult feline caudate nucleus: comparison to fetal lesions

After a unilateral resection of the frontal cortex in fetal cats the volume of the caudate nucleus increases while the packing density of neuronal and glial cells does not change. In the present report we address the questions of whether a similar lesion sustained neonatally or a more extensive neodecortication sustained neonatally or in adulthood may have the same unusual effect. Stereological methods were used to determine bilaterally the volume of the caudate nucleus as well as to estimate the total number and packing density of neurons and glial cells in the caudate nucleus ipsilateral to the lesion. Comparisons between each of three experimental groups and intact animals were made at a time when all animals were young adults. In cats with a unilateral frontal cortical lesion performed between postnatal days 8 and 14, none of the measured parameters changed significantly compared to intact controls. In cats with removal of the entire left neocortex in adulthood, the ipsilateral caudate nucleus volume decreased by 18.1% and by 21.5% relative to intact and to neonatal hemidecorticated cats respectively (P < 0.05), with no change in the contralateral caudate. In the ipsilateral caudate the total number of neurons decreased by 21.8% (P < 0.05) compared to controls while the number of glial cells did not change significantly. In the same caudate the packing density of neurons did not change significantly (except for a 17.1% decrease, P < 0.05, relative to frontal-lesioned cats) while that of glial cells increased by 19.9% and by 24.7% compared to intact and neonatal neodecorticated cats respectively (P < 0.05). In adult cats in which a similar hemineodecortication was performed between postnatal days 8 and 13, the only significant changes were a 25.8% (P < 0.05) and a 30.6% (P < 0.05) decrease in neuron packing density compared to intact and frontal-lesioned cats, respectively. In summary, a restricted unilateral neocortical resection in neonatal cats did not induce any morphological changes in the caudate nucleus that we could detect with the methods employed. In contrast, an extensive neodecortication sustained in adulthood produced ipsilateral caudate shrinkage with substantial neuron loss and increase in packing density of glial cells, while a similar lesion but sustained neonatally only altered substantially the packing density of glial cells (decreased). Therefore, we concluded that (i) the caudate nucleus hypertrophy which we reported after a unilateral discrete cortical removal during the prenatal period is a unique phenomenon which is peculiar to the cat brain during the last third of gestation; (ii) the caudate nucleus changes seen in the cats with hemineodecortication in adulthood are degenerative in nature and closely resemble those which we reported for other subcortical nuclei following a similar lesion; and (iii) the animals with neonatal hemidecortication are relatively spared from these degenerative effects. Overall, these results indicate that, as for other structures, the morphological changes of the caudate nucleus following neocortical damage depend on the maturational state of the brain at the time of the injury and on the size of the lesion, and support the notion that the consequences of cerebral cortex lesions upon subcortical brain nuclei are of a different nature when sustained in prenatal as compared to postnatal cats.

Intrastriatal injection of a muscarinic receptor agonist and antagonist regulates striatal neuropeptide mRNA expression in normal and amphetamine-treated rats

Systemic administration of the muscarinic receptor antagonist, scopolamine, augments, whereas the muscarinic receptor agonist, oxotremorine, attenuates behaviors (locomotion and stereotypies) and preprodynorphin (PPD) and substance P (SP) gene expression in striatonigral neurons induced by the indirect dopamine receptor agonist, amphetamine (AMPH). In contrast, systemic scopolamine blocks, whereas oxotremorine augments, AMPH-stimulated preproenkephalin (PPE) gene expression in striatopallidal neurons. This study investigated the site of action of these effects by administering scopolamine and oxotremorine directly into the striatum and assessing the expression of neuropeptide mRNAs with quantitative in situ hybridization. Unilateral injection of scopolamine into the dorsal striatum augmented, and oxotremorine attenuated, AMPH (2.5 mg/kg, i.p.)-stimulated behaviors. Intrastriatal scopolamine at a concentration of 62 mM, but not 6.2 mM, increased basal levels of PPD and SP mRNAs in the dorsal striatum. In addition, both 6.2 and 62 mM scopolamine significantly augmented AMPH-stimulated PPD and SP mRNA levels. Intrastriatal infusion of 1.6 or 8.1 mM oxotremorine did not alter basal levels of striatal PPD and SP mRNAs. However, both concentrations of oxotremorine completely blocked AMPH-stimulated SP mRNA and oxotremorine at 8.1 mM blocked AMPH-stimulated PPD mRNA. In contrast, PPE induction by AMPH was blocked by 62, but not 6.2, mM scopolamine. Both concentrations of oxotremorine tended to augment basal and AMPH-stimulated PPE mRNA in the dorsal striatum but the trend was not significant. These data demonstrate an inhibition of striatonigral, and facilitation of striatopallidal, gene expression through activation of local striatal muscarinic receptors, which is consistent with the changes seen after systemic administration of muscarinic agents. Therefore, muscarinic cholinergic regulation of basal and stimulated expression of neuropeptide mRNA is processed within the striatum.

Synaptic integration of functionally diverse pallidal information in the entopeduncular nucleus and subthalamic nucleus in the rat

To determine the principles of synaptic innervation of neurons in the entopeduncular nucleus and subthalamic nucleus by neurons of functionally distinct regions of the pallidal complex, double anterograde labeling was carried out at both light and electron microscopic levels in the rat. Deposits of the anterograde tracers Phaseolus vulgaris-leucoagglutinin and biotinylated dextran amine were placed in different functional domains of the pallidal complex in the same animals. The tracer deposits in the ventral pallidum and the globus pallidus gave rise to GABA-immunopositive projections to the entopeduncular nucleus, the subthalamic nucleus, and the more medial lateral hypothalamus that were largely segregated but overlapped at the interface between the two fields of projection. In these regions the proximal parts of individual neurons in the entopeduncular nucleus, lateral hypothalamus, and subthalamic nucleus received synaptic input from terminals derived from both the ventral pallidum and the globus pallidus. Furthermore, the analysis of the afferent synaptic input to the dendrites of neurons in the subthalamic nucleus that cross functional boundaries of the nucleus defined by the pallidal inputs, revealed that terminals with the morphological and neurochemical characteristics of those derived from the pallidal complex make synaptic contact with all parts of the dendritic tree, including distal regions. It is concluded that functionally diverse information carried by the descending projections of the pallidal complex is synaptically integrated by neurons of the entopeduncular nucleus, lateral hypothalamus, and subthalamic nucleus by two mechanisms. First, neurons located at the interface between functionally distinct, but topographically adjacent, projections could integrate diverse information by means of the synaptic convergence at the level of the cell body and proximal dendrites. Second, because the distal dendrites of neurons in the subthalamic nucleus receive input from the pallidum, those that extend across two distinct domains of pallidal input could also provide the morphological basis of integration.

Phenotypic characterization of neurotensin messenger RNA-expressing cells in the neuroleptic-treated rat striatum: a detailed cellular co-expression study

The chemical phenotype of proneurotensin messenger RNA-expressing cells was determined in the acute haloperidol-treated rat striatum using a combination of (35S)-labelled and alkaline phosphatase-labelled oligonucleotides. Cellular sites of proneurotensin messenger RNA expression were visualized simultaneously on tissue sections processed to reveal cellular sites of preproenkephalin A messenger RNA or the dopamine and adenylate cyclase phosphoprotein-32, messenger RNA. The cellular co-expression of preproenkepahlin A (enkephalin) and preprotachykinin (substance P) messenger RNA was also examined within forebrain structures. Cellular sites of enkephalin (substance P) and dopamine and adenylate cyclase phosphoprotein-32 messenger RNAs were visualized using alkaline phosphatase-labelled oligonucleotides whilst sites of substance P and proneurotensin messenger RNA expression were detected using (35S)-labelled oligos. Cellular sites of enkephalin and dopamine and adenylate cyclase phosphoprotein-32 gene expression were identified microscopically by the concentration of purple alkaline phosphatase reaction product within the cell cytoplasm, whereas sites of substance P and proneurotensin gene expression were identified by the dense clustering of silver grains overlying cells. An intense hybridization signal was detected for all three neuropeptide messenger RNAs in the striatum, the nucleus accumbens and septum. Dopamine and adenylate cyclase phosphoprotein-32 messenger RNA was detected within the neostriatum but not within the septum. In all forebrain regions examined, with the exception of the islands of Calleja, the cellular expression of enkephalin messenger RNA and substance P messenger RNA was discordant; the two neuropeptide messenger RNAs were detected essentially in different cells, although in the striatum and nucleus accumbens occasional isolated cells were detected which contained both hybridization signals; dense clusters of silver grains overlay alkaline phosphatase-positive cells, demonstrating clearly that these dual-labelled cells expressed both messenger RNAs. By contrast, the hybridization signals for proneurotensin and enkephalin, and proneurotensin and dopamine and adenylate cyclase phosphoprotein-32 were generally coincident, at least within the neostriatum; most proneurotensin messenger RNA-positive cells expressed enkephalin messenger RNA and were also positive for dopamine and adenylate cyclase phosphoprotein-32 messenger RNA. However, occasional proneurotensin messenger RNA-positive striatal cells were identified that were single-labelled and did not express enkephalin messenger RNA. Within the septal nucleus, enkephalin messenger RNA and substance P messenger RNA were expressed essentially within segregated cell populations. These studies illustrate further the utility of co-expression techniques for investigating the chemical phenotype of cells within the CNS and demonstrate that the distribution of neuropeptide co-expressing cells is different within different brain regions. That several populations of proneurotensin messenger RNA-positive striatal cells may exist, of which one population is sensitive to haloperidol, co-expresses enkephalin messenger RNA and is positive for dopamine and adenylate cyclase phosphoprotein-32 messenger RNA may be of some significance in neuropsychiatric/neurological disorders given that the translated peptide, neurotensin, is known to influence and interact closely with the dopamine systems.

Repeated injections of dizocilpine maleate (MK-801) do not suppress the effects of nigrostriatal dopamine deafferentation on glutamate decarboxylase (GAD67) mRNA expression in the adult rat striatum

The present study examined the effects of glutamate transmission blockade through N-methyl-D-aspartate (NMDA) receptor subtype by repeated administration of dizocilpine maleate (0.2 mg/kg. i.p., twice a day for eight days) alone or in combination with unilateral 6-hydroxydopamine-induced lesion of the nigrostriatal dopaminergic pathway on GABAergic neurons in the adult rat striatum. For this purpose, the expression of the messenger RNA encoding for the 67 kDa isoform of the GABA synthesizing enzyme, glutamate decarboxylase (GAD67 mRNA), was studied in the various conditions by quantitative in situ hybridization. The dizocilpine maleate treatment alone did not induce significant change of GAD67 mRNA levels in the striatum, indicating that NMDA receptors may not have a major role in the transcriptional regulation of GAD67 in the adult rat striatum. As reported previously, the unilateral dopaminergic lesion resulted in marked increases in GAD67 mRNA levels in the ipsilateral striatum. This up-regulation was not significantly affected by the treatment with dizocilpine maleate started 12 days after the unilateral intranigral 6-hydroxydopamine injection. Therefore, NMDA receptors are unlikely to contribute to the dopamine lesion-induced GAD67 mRNA up-regulation in striatal projection neurons. This result is of major interest in comparison with our previous finding that NMDA receptor activation is necessary to maintain the up-regulation of enkephalin expression in the striatum after dopamine lesion.

The contralateral cortex contributes to the effects of hemidecortication on neuropeptide Y immunoreactivity in the rat striatum

We have previously shown that unilateral lesion by thermocoagulation of sensori-motor cortex which provides excitatory afferents to the striatum increases the number of neuropeptide Y (NPY)-immunoreactive neurons in the rat striatum. The present study examined whether this paradoxical effect is due to adaptive neuronal mechanisms involving the crossed projections from the contralateral spared cortex. To test this hypothesis, we compared the effects of unilateral and bilateral cortical lesions on the number of NPY-immunoreactive neurons in the striatum. Results showed that animals with bilateral lesion have no significant change in NPY immunoreactivity versus control suggesting that the contralateral intact cortex is responsible for the increase of NPY-immunoreactive neurons detected after unilateral lesion.

Efferent connections of the caudal part of the globus pallidus in the rat

The efferent connections of the caudal pole of the globus pallidus (GP) were examined in the rat by employing the anterograde axonal transport of Phaseolus vulgaris leucoagglutinin (PHA-L), and the retrograde transport of fluorescent tracers combined with choline acetyltransferase (ChAT) or parvalbumin (PV) immunofluorescence histochemistry. Labeled fibers from the caudal GP distribute to the caudate-putamen, nucleus of the ansa lenticularis, reuniens, reticular thalamic nucleus (mainly its posterior extent), and along a thin strip of the zona incerta adjacent to the cerebral peduncle. The entopeduncular and subthalamic nuclei do not appear to receive input from the caudal GP. Descending fibers from the caudal GP course in the cerebral peduncle and project to posterior thalamic nuclei (the subparafascicular and suprageniculate nuclei, medial division of the medial geniculate nucleus, and posterior intralaminar nucleus/peripeduncular area) and to extensive brainstem territories, including the pars lateralis of the substantia nigra, lateral terminal nucleus of the accessory optic system, nucleus of the brachium of the inferior colliculus, nucleus sagulum, external cortical nucleus of the inferior colliculus, cuneiform nucleus, and periaqueductal gray. In cases with deposits of PHA-L in the ventral part of the caudal GP, labeled fibers in addition distribute to the lateral amygdaloid nucleus, amygdalostriatal transition area, cerebral cortex (mainly perirhinal, temporal, and somatosensory areas) and rostroventral part of the lateral hypothalamus. Following injections of fluorescent tracer centered in the lateral hypothalamus, posterior intralaminar nucleus, substantia nigra, pars lateralis, or lateral terminal nucleus, a substantial number of retrogradely labeled cells is observed in the caudal GP. None of these cells express ChAT immunoreactivity, but, except for the ones projecting to the lateral hypothalamus, a significant proportion is immunoreactive to PV. Our results indicate that caudal GP efferents differ from those of the rostral GP in that they project to extensive brainstem territories and appear to be less intimately related to intrinsic basal ganglia circuits. Moreover, our data suggest a possible participation of the caudal GP in feedback loops involving posterior cortical areas, posterior striatopallidal districts, and posterior thalamic nuclei. Taken as a whole, the projections of the caudal GP suggest a potential role of this pallidal district in visuomotor and auditory processes.

Representation of a single vibrissa in the rat neostriatum: peaks of energy metabolism reveal a distributed functional module

In unanaesthetized rats, mechanical stimulation of a single vibrissa increased glucose utilization in one cortical column of the somatosensory area and in several spots in the dorsolateral neostriatum, predominantly on the side contralateral to the stimulation. Two or three peaks of glucose utilization unique to the stimulated animals were seen in cross sections throughout a 1.8 mm anteroposterior extent in the dorsolateral striatum. These observations suggest that one cortical column is functionally related to several neostriatal regions. The distributed modularity may be an important characteristic of the basal ganglia system.

Dissociable effects of anterior and posterior cingulate cortex lesions on the acquisition of a conditional visual discrimination: facilitation of early learning vs. impairment of late learning

Two experiments investigated the effects of quinolinic acid induced lesions of the anterior and posterior cingulate cortices on the acquisition and performance of a conditional visual discrimination (CVD) task, in which rats were required to learn a rule of the type: "If lights are flashing FAST, press the right lever; if SLOW press left". In Experiment 1, animals with lesions of the anterior cingulate cortex (ANT group) demonstrated a significant enhancement in learning during the early stages of task acquisition. Conversely, animals with lesions of the posterior cingulate cortex (POS group) were impaired in learning during the later stages of acquisition. There were no significant differences between the ANT and POS groups on the performance of the task when either variable inter-trial intervals or reduced stimulus durations were imposed. In Experiment 2, the specificity of the lesion effects for processes operative during the early and late stages of learning was tested. Animals were trained to a criterion of 70% correct choices on two consecutive sessions prior to lesioning, and subsequently allowed to continue to acquire the task to the mean asymptotic performance level of 85% correct choices on two consecutive sessions. Animals of the POS group were impaired in learning during this later stage of task acquisition, thus replicating the pattern of results obtained in Experiment 1. The animals in Experiment 2 were then tested following a 30-day retention interval and during extinction (removal of sucrose from the magazine). The extinction test revealed an impairment in the ability of animals in the ANT group to omit lever responses in the absence of reinforcement. These results indicate that the anterior and posterior cingulate cortices are functionally dissociable, and suggest that they may form part of complementary, but competing, learning and memory systems.

Lack of cross-tolerance between haloperidol and clozapine towards Fos-protein induction in rat forebrain regions

We investigated whether the acute effects of haloperidol and clozapine on Fos expression in the rat forebrain are mediated by the same receptors through evaluation of cross-tolerance, particularly in the commonly affected areas. Acutely administered haloperidol (1 mg/kg. i.p.) and clozapine (20 mg/kg, i.p.) induce regionally different (e.g., the striatum, the hypothalamic paraventricular and supraoptic nuclei, and the central amygdala) and overlapping (e.g., the nucleus accumbens and the lateral septum) patterns of Fos-protein distribution in the rat forebrain. After long-term treatment, part of the acute effects of these drugs disappears in most brain areas, except in the lateral septum, the hypothalamic paraventricular and supraoptic nuclei and the amygdala following haloperidol administration. Cross-tolerance between haloperidol and clozapine was determined by administering a challenge dose of the one antipsychotic, following a 21-day pretreatment with the same or the other drug or saline. In none of the investigated brain regions was cross-tolerance towards Fos-protein induction found after haloperidol challenge in the clozapine-treated rats. Conversely, a competitive dose of clozapine in long-term haloperidol-treated rats showed cross-tolerance in the lateral septum, while the common effect of the drugs in both the dorsomedial and the dorsolateral parts of the striatum was very small. These findings indicate that, for the major part, the responses to haloperidol and clozapine are mediated by different receptors, even in brain areas that are affected by both drugs.

Neocortical damage alters synaptic responses of neostriatal neurons in vitro

The present experiments were designed to investigate the physiological impact of a partial decortication upon neostriatal synaptic responses using intracellular recording techniques in the in vitro brain slice preparation. In the intact rat, the locally evoked neostriatal synaptic response is primarily mediated by excitatory amino acid receptor activation. Following neocortex damage, the contributions of both N-methyl-D-aspartate and non-N-methyl-D-aspartate receptor activation were significantly diminished, although responses remained robust in amplitude and duration. Components of the locally evoked synaptic response mediated by activation of GABAA receptors were relatively unchanged, while presynaptic inhibition mediated by activation of GABAB receptors was markedly reduced. Furthermore, the normally minimal acetylcholine contribution to the synaptic response was significantly increased after neocortical damage. This enhanced cholinergic role in the generation of the synaptic response appeared to be mediated primarily by activation of nicotinic receptors. Thus, neocortical damage leads to novel physiological relationships between intrinsic neostriatal cholinergic interneurons and the GABAergic projection neurons. One possibility is that cholinergic interneurons have the potential for substituting for the loss of excitation created by the absence of neocortical glutamatergic input.

Corticostriatal innervation of the patch and matrix in the rat neostriatum

The distribution of rat corticostrial axons in the patch (striosome) and matrix compartments of the neostriatum was studied by using axonal labeling with biotinylated dextran amine (BDA) and identifying patch and matrix in the same section with calbindin immunocytochemistry. Small injections of BDA were made in the anterior cingulate, medial agranular, lateral agranular, or somatosensory cortex. Each area projected to both the patch and matrix compartments, except for the somatosensory cortex, which had only matrix projections. Within the remaining cortical areas, injections in layers Vb and VI preferentially labeled axons in patches whereas injections in layers III-Va preferentially labeled matrix axons. Axons from these injections formed varicosities preferentially, but not exclusively, in one compartment. There was a population of axons that crossed compartmental boundaries and arborized in both patch and matrix. Two distinct patterns of corticostriatal axonal arborizations were observed. Small, discrete foci of innervation were seen in the patch compartment and in some regions of the matrix. The focal arborizations in the matrix were observed through the rostrocaudal extent of the neostriatum but were most obvious in the caudal one-third. They resembled the matrisomes observed in cat and primate corticostriatal projections. The second pattern of innervation consisted of extended axonal arborizations that covered large regions of the rostral neostriatal matrix. These results support the concept of multiple classes of corticostriatal neurons having different targets within the neostriatum, following different topographical rules, and having different but overlapping distributions across cortical areas.

Opioid receptor ligand binding in the human striatum: II. Heterogeneous distribution of kappa opioid receptor labeled with [3H]bremazocine

Selective kappa opioid receptor autoradiography with [3H]bremazocine (BRM) was used to examine regional and subregional kappa receptor distribution patterns at five rostrocaudal levels through the human striatum. [3H]BRM binding densities were measured in the individual striatal nuclei and in subregions therein. The distribution of [3H]BRM binding sites was found to have a strongly heterogeneous character. At the regional level a rostral-to-caudal decrease in [3H]BRM binding densities was observed. Also, a dorsal-to-ventral differentiation was seen, with higher values in the ventral striatum, especially in the nucleus accumbens, and lower values in the dorsal parts of the caudate nucleus and putamen. These findings suggest an association of kappa receptor function with limbic-related processes in the ventral striatum. Along the ventral edge of the nucleus accumbens and putamen, specific domains with extremely high [3H]BRM binding values were identified.

Altered Fos-like immunoreactivity in terminal regions of the mesotelencephalic dopamine system is associated with reappearance of tyrosine hydroxylase immunoreactivity at the sites of focal 6-hydroxydopamine lesions in the nucleus accumbens

The present study was undertaken in order to determine whether unilateral 6-hydroxydopamine (6-OHDA) lesions in the nucleus accumbens (Acb) affect basal Fos-like immunoreactivity (-LI) in terminal regions of the mesotelencephalic dopamine system. It was hypothesized that dopamine depletion in the Acb would alter activation of mesotelencephalic dopamine neurons perhaps via the striatomesencephalic GABAergic pathway, and that this may be detected as altered basal Fos-LI in mesotelencephalic terminal regions. 6-OHDA treatment effectively depleted tyrosine hydroxylase (TH)-LI in well-circumscribed areas of the Acb at 14 days post-lesion, but at 25 days post-lesion all animals showed a reappearance of TH-LI staining in the lesioned region. When data from a number of mesotelencephalic terminals regions was pooled. Fos-LI cell density was higher in the sham and lesion 14-day groups and sham 25-day group than both the 25-day lesion group and untreated controls. The present study demonstrates that unilateral sham and 6-OHDA lesions in the Acb may have repercussions throughout the mesotelencephalic dopamine system. Further investigation is necessary to determine whether reappearance of TH-LI at the lesion site contributes to the return of Fos-LI to basal levels.

Anatomical and functional evidence for lesion-specific sprouting of corticostriatal input in the adult rat

Previous studies in our laboratory have shown that cortical lesions induced by thermocoagulation of pial blood vessels, but not by acute aspiration, result in 1) the preservation of control levels of the growth-associated protein (GAP)-43 and 2) a prolonged increase in neurotransmitter gene expression in the denervated dorsolateral striatum. We have examined whether corticostriatal projections from the spared homotypic contralateral cortex contribute to these effects. Adult rats received either a thermocoagulatory or aspiration lesion of the cerebral cortex and, after 30 days, received an injection of the anterograde tracer, Fluoro-Ruby, in the contralateral homotypic cortex. Rats were killed 7 days later, and labeled fibers were examined with fluorescence microscopy in the ipsilateral and contralateral striata. Ipsilateral corticostriatal projections were detected in lesioned and unlesioned rats. Numerous labeled fibers were detected in the contralateral striatum of thermocoagulatory-lesioned but not aspiration-lesioned or control animals, suggesting that contralateral cortical neurons may undergo axonal sprouting in the denervated striatum following a thermocoagulatory lesion of the cortex. To determine whether contralateral corticostriatal fibers play a role in the changes in striatal gene expression induced by the thermocoagulatory lesions, the effects of aspiration lesions, as well as unilateral and bilateral thermocoagulatory lesions of the cortex were compared. Confirming previous results, striatal enkephalin mRNA levels were increased after a unilateral thermocoagulatory lesion. However, they were unchanged after aspiration or bilateral thermocoagulatory lesions, suggesting that sprouting or overactivity of contralateral corticostriatal input contributes to the increase seen after unilateral thermocoagulatory lesions.

Involvement of the caudal striatum in auditory processing: c-fos response to cortical application of picrotoxin and to auditory stimulation

The topographical organization of corticostriatal connections have been postulated to follow a longitudinal pattern, each cortical area projecting on a longitudinal strip stretching along the whole rostro-caudal axis of the striatum. However, compared to the rostral striatal region, the caudal striatum exhibits distinct features in terms of connectivity and neuronal phenotype. The induction of c-fos expression in the striatum by cortical activation or sensory stimulation may throw more light on these functional corticostriatal relationships. In the present study, we examined the effects of cortical activation by local application of picrotoxin on the Fos-immunoreactivity (Fos-IR) in the striatum of the mouse, with special reference to the caudal part of the striatum. Activation of the auditory cortex induced a dense ipsilateral Fos-IR restricted to the caudal striatum i.e., in the caudo-medial striatum and in the caudal part of fundus striati, and a very sparse labelling in the medial region of the rostral striatum. Conversely, activation of both sensori-motor and visual cortices only resulted in Fos-IR in the main rostral part of the striatum, without response in the caudal extremity of the striatum. On the other hand, visual or auditory stimulation in awake animals failed to induce c-fos expression in the striatum. However, using quantitative in-situ hybridization for c-fos mRNA, we found that auditory, but not visual stimulation significantly potentiated the c-fos response to the D1 agonist SKF 38393 (2 mg/kg, i.p.) in the caudal part of the striatum. These functional observations suggest that, despite a more widespread cortico-striatal connection pattern deduced from tracing experiments, the strongest functional projections from the auditory system mainly converge onto a restricted part of the caudal striatum, according to a connection pattern that is reminiscent of the transverse segmentation proposed in early lesioning studies of corticostriatal projections.

Skilled motor deficits in rats induced by ventrolateral striatal dopamine depletions: behavioral and pharmacological characterization

Rats were tested in an instrumental lever pressing procedure, in which a computer program recorded detailed parameters of responding such as response initiation and duration. Initially, rats with ventrolateral striatal dopamine depletions and control rats were tested on days 3-5 after surgery. Dopamine depletions produced by local injections of 6-hydroxydopamine substantially reduced the number of lever presses emitted. Dopamine depleted animals showed significant increases in average response initiation times, average length of fast initiation times, average length of pauses and total pause time. The distribution of initiation times was altered so that DA depleted rats showed significant reductions in the relative number of very high rate responses and also showed increases in the relative number of pauses. On day 7 after surgery, dopamine-depleted rats received one of three drug treatments: injections of ascorbate vehicle, injections of 20.0 mg/kg L-DOPA, and injections of 40.0 mg/kg L-DOPA. Injections of 40.0 mg/kg L-DOPA led to some improvement in several parameters of instrumental responding. Compared to the previous baseline day, the group that received 40.0 mg/kg L-DOPA showed a significant increase in number of responses on the drug treatment day, and also showed significant decreases in average response initiation time and total pause time. The group that received 40.0 mg/kg L-DOPA also showed significant increases in number of responses (expressed as a percent of the previous day) when compared to the control group that received injections of ascorbate vehicle. These results indicate that L-DOPA can partially reverse the skilled motor deficits produced by ventrolateral striatal dopamine depletions, and suggest that this test may be useful for the assessment of antiparkinsonian drugs.

Thalamic collaterals of corticostriatal axons: their termination field and synaptic targets in cats

Branched cortical projections to the thalamus and striatum were investigated in cats by injecting the retrograde-anterograde tracer biotinylated-dextran amine (BDA) into the caudate nucleus. These injections gave rise to plexuses of labeled fibers and varicosities in widespread thalamic territories. For instance, the lateroposterior nucleus and pulvinar (LP-PUL) mostly contained thick axons that contributed clusters of large-sized varicosities, each forming multiple asymmetric synapses, usually with vesicle-filled dendrites. In contrast, the intralaminar nuclei mostly contained thin axonal segments that emitted small en passant varicosities that formed single asymmetric synapses with spines. Because the caudate nucleus does not project to the thalamus, this labeling had to arise from a neuronal population with branching axons to both structures. Previous findings pointed to three possible sources: brainstem monoaminergic cells, intralaminar thalamic neurons, and corticostriatal cells. The first candidate could be ruled out because monoaminergic neurons contribute small-sized terminals that usually lack membrane specializations. The second possibility was discarded because retrograde tracer injections into the LP-PUL did not give rise to retrograde labeling in the intralaminar nuclear complex but to massive retrograde labeling in deep layers of cortical areas 5 and 7. Therefore, we concluded that the thalamic anterograde labeling originated from corticostriatal neurons, with axons branching to the thalamus. In keeping with this conclusion, Phaseolus vulgaris-leucoagglutinin (PHA-L) injections into cortical areas 5-7 labeled a group of thick corticothalamic fibers that ended in clusters of large boutons in the LP-PUL. These PHA-L-positive terminals were indistinguishable from those labeled after injections of BDA into the caudate nucleus, but they were easy to distinguish from the typical corticothalamic fibers. These findings indicate that the cerebral cortex could coordinate the activity of the striatum and the thalamus via a rich axonal network that collateralizes to both structures. The extent and synaptic organization of this branched projection impose a revision of the traditional scheme of thalamic connectivity.

Functional brain reorganization in children

Developmental brain plasticity in association with focal brain injury is dependent on a number of factors, including age of the individual at the time of injury, size and topography of the brain lesion, maturational state of the brain system injured, integrity of brain areas surrounding and contralateral to the lesion, presence and duration of epilepsy, and medication effects. Recently developed functional neuroimaging tools now make it possible to study non-invasively several aspects of human brain functional reorganization in response to injury. Clinical models which are suitable for the study of developmental brain plasticity include patients who have undergone cortical resections for the alleviation of intractable epilepsy, patients who have sustained unilateral cerebrovascular insults at various periods of development, patients with chronic progressive unilateral brain injury such as in the Sturge-Weber syndrome, and patients with early sensory deprivation such as blind or deaf subjects. Although evidence of functional brain reorganization can be demonstrated in these models, it is emphasized that the neurobiological rules that govern intrahemispheric versus interhemispheric reorganization of function in the brain are, at present, poorly understood.

Traumatic brain injury of the forelimb and hindlimb sensorimotor areas in the rat: physiological, histological and behavioral correlates

This study characterizes physiological, histological and behavioral effects of traumatic brain injury (TBI) produced by a controlled pneumatic impactor striking the entire right sensorimotor cortex of the anesthetized rat. Damage to both the fore- and hindlimb sensorimotor areas resulted in a hemiparetic animal which allowed us to use four sensitive behavioral/neurological tests to track the recovery sequelae after injury. Initial experiments measured cardiovascular and respiratory effects after cortical impact which depressed the dura to varying depths. Both 0.5 mm and 1 mm cortical depressions produced a momentary decrease (P < 0.05) in mean arterial blood pressure (MABP) while cortical impacts to depths of 2 mm or 3 mm produced a momentary increase (P < 0.05) in MABP. Normotension was re-established within 30 s after the initial response at all injury levels. Respiratory rate was affected only following 3 mm cortical depressions. A 1 mm cortical depression appeared ideal in terms of minimal cardiorespiratory effects, low mortality and lasting behavioral effects. For behavioral and histologic studies, therefore, additional rats were injured by a 1 mm cortical impact and tested for 8 weeks after TBI using four behavioral tests. Injured rats displayed both fore- and hindlimb deficits up to 56 days while traversing a narrow beam (P < 0.001) and up to 28 days when crossing a pegged beam (P < 0.05). Forelimb deficits evaluated on a wire grid platform were evident for 28 days (P < 0.05). Forepaw preference measured in a non-test setting indicated a bias to use the unaffected forepaw for 35 days (P < 0.05). A biphasic pattern of functional recovery was seen on all tests. A period of rapid functional recovery lasting 7 to 10 days was followed by a slower period of functional recovery lasting many weeks. Possible meanings of this biphasic recovery are discussed as issues of behavioral compensation/adaptation versus true neural recovery. Eight weeks after TBI histological analyses indicated that axonal degeneration was present in the areas adjacent to the ipsilateral cortical injury site. Degenerating fibers also extended across the corpus callosum into the homologous area in the contralateral cortex and were seen in the ipsilateral striatum, somatosensory and motor thalamic nuclei and substantia nigra. Significant axonal degeneration occurred bilaterally around the deep cerebellar nuclei. Degenerating fibers extended into the folia and terminated in the cerebellar granule cell layer. Thus the entire sensorimotor control system appeared to have been affected by a cortical injury.

Changes in [3H]AMPA and [3H]kainate binding in rat caudate-putamen and nucleus accumbens after 6-hydroxydopamine lesions of the medial forebrain bundle: an autoradiographic study

The binding parameters of [3H] alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionate (AMPA) and [3H]kainate binding were examined in caudate-putamen and nucleus accumbens of rat striatum after unilateral lesions of the right medial forebrain bundle (MFB) using in vitro receptor autoradiography. Lesioning of the dopaminergic fibres in the MFB with 6-hydroxydopamine (6-OHDA) resulted, after one or four weeks, in a significant decrease in the levels of [3H]GBR 12935 (1-[2-diphenylmethoxy)-ethyl]-4-(3-phenylpropyl) piperazine) in ipsilateral caudate-putamen and nucleus accumbens (62 and 43%, respectively). A comparison of the dissociation constants (Kd) of [3H]AMPA and [3H]kainate binding in caudate-putamen and nucleus accumbens between control and MFB-lesioned side did not indicate any significant change. However, the maximum number of [3H]AMPA and [3H]kainate binding sites (Bmax) were significantly decreased in caudate-putamen and nucleus accumbens of the MFB-lesioned side of the brain. This decrease was between 17 and 26%. Our results suggested that at least one-fourth to one-fifth of AMPA and kainate receptors in rat caudate-putamen and nucleus accumbens are localized on the presynaptic endings of dopamine fibres that follow the MFB. A role of non-NMDA glutamate receptors in the presynaptic regulation of dopamine release in rat striatum is therefore supported.

The lamellar organization of the rat substantia nigra pars reticulata: segregated patterns of striatal afferents and relationship to the topography of corticostriatal projections

The striatonigral pathway provides one of the most direct routes for information flow through the basal ganglia system. Via this pathway information from sensory, motor and associative areas of the cerebral cortex are routed to a variety of thalamocortical and brainstem networks involved in the organization of motor behaviour. In a previous analysis of the rat substantia nigra pars reticulata we have shown that the nigral cells which project to thalamus, tectum and tegmentum are topographically ordered along a series of curved laminae. Extending these observations, the present study examined how striatal regions related to particular areas of the cerebral cortex innervate the lamellar keyboard of nigral output neurons. For this purpose, small microiontophoretic injections of wheat germ agglutinin conjugated to horseradish peroxidase were performed in the striatum and the distribution of retrogradely-labelled cells in the cerebral cortex and anterogradely-labelled axons in the substantia nigra were conjointly examined. The results indicate that with the exception of the striatal region related to the allocortex, all the various components of the striatal functional mosaic are represented in the substantia nigra pars reticulata. This representation is organized under the form of longitudinal bands which compose a series of curved laminae enveloping a core located dorsolaterally in the substantia nigra. The striatal mapping in substantia nigra pars reticulata is such that the projections of the auditory and visual compartments are confined to the most ventral lamina. More dorsally, an ordered representation of the body is achieved by the nigral lamination. The oral and perioral body parts are centred on the dorsolateral core and the more distal parts of the face and limbs are progressively set out in more peripheral laminae. In the region affiliated to the prefrontal cortex, the dorsal cingulate district innervate a ventromedial lamina, the prelimbic/insular district lie dorsal to it. Projections from lateral orbital and insular compartments extend laterally along the dorsal margin of the pars reticulata. Since the "onion-like" distribution of striatal inputs is precisely the form observed in the distribution of nigral efferent neurons, the present observations favour the view that the nigral lamination underlies formation of specific input-output channels of processing. Evidence is considered that these channels are specialized for particular classes of movements or behaviours and integrate the various information relevant to the completion of these movements or behaviours.

Ventral pallidostriatal pathway in the monkey: evidence for modulation of basal ganglia circuits

This study describes the organization of the ventral and dorsal pallidostriatal pathway in the monkey. Both retrograde and anterograde tracers were injected into various regions of the ventral and dorsal pallidum as well as into the striatum. The data indicate that the pallidostriatal pathway is an extensive pathway in the monkey. The projections are organized in a topographic manner preserving a general, but not strict medial-to-lateral and ventral-to-dorsal organization. The terminal arrangement of pallidostriatal fibers is widespread. Non-adjacent pallidal regions send fibers to the striatum which overlap considerably, suggesting convergence of terminals from different pallidal regions. The pallidostriatal pathway is found to have a reciprocal but also a large non-reciprocal component to the striatopallidal pathway. On the basis of these data it is concluded that segregation of different corticobasal ganglia-cortical pathways is maintained in the striatopallidal direction as described earlier (Haber et al. [1990] (J. Comp. Neurol. 293:282-298). However, the pallidostriatal projection to a large region of the striatum allows the modulation of several cortico-basal ganglia circuits.

Patterns of overlap and segregation between insular cortical, intermediodorsal thalamic and basal amygdaloid afferents in the nucleus accumbens of the rat

Regions of the prefrontal cortex that project to the nucleus accumbens in the rat receive input from midline thalamic and basal amygdaloid nuclei which also project to the same striatal region as their prefrontal cortical target. For example, the prelimbic cortex projects to the medial nucleus accumbens, and receives input from the paraventricular thalamic nucleus and the parvicellular basal amygdala. These latter two areas also project to the medial nucleus accumbens. It has been shown that afferents from the prelimbic cortex, the paraventricular thalamic nucleus and the parvicellular basal amygdala to the nucleus accumbens overlap or are separated in the nucleus accumbens, depending upon their position in the shell and core. The dorsal agranular insular cortex, the intermediodorsal thalamic nucleus and the magnocellular basal amygdaloid nucleus terminate in the lateral part of the nucleus accumbens and adjacent ventral part of the caudate-putamen. The intermediodorsal thalamic nucleus and the magnocellular basal amygdaloid nucleus reach both the dorsal agranular insular cortex and the lateral nucleus accumbens, and thus appear positioned to influence the prefrontal corticostriatal system at cortical and striatal levels. However, all three afferent systems have a heterogeneous distribution within this striatal region, and whether these projections actually reach the same areas is unknown. We investigated the patterns of separation and overlap in the nucleus accumbens between dorsal agranular insular cortical, magnocellular basal amygdaloid and intermediodorsal thalamic afferents with respect to the histochemical features of the nucleus. Techniques allowing the detection of two different anterograde tracers, or a single anterograde tracer and Calbindin-D28k immunoreactivity, in the same tissue sections were used. The results demonstrate that the afferents from the dorsal agranular insular area and the intermediodorsal thalamic nucleus avoid the shell of the lateral nucleus accumbens, which receives strong inputs from the magnocellular basal amygdala. In the matrix of the core and the ventral part of the caudate-putamen, fibers from the superficial layers of the dorsal agranular insular area overlap precisely with afferents from the intermediodorsal nucleus. In the patches, projections from the deep layers of the dorsal agranular insular cortex coincide with those from the magnocellular basal amygdala. The present findings have implications for the compartmental structure of the nucleus accumbens and provide novel insights into the organizational principles of prefrontal corticostriatal circuits.

Implementation of action sequences by a neostriatal site: a lesion mapping study of grooming syntax

The neostriatum and its connections control the sequential organization of action ("action syntax") as well as simpler aspects of movement. This study focused on sequential organization of rodent grooming. Grooming syntax provides an opportunity to study how neural systems coordinate natural patterns of serial order. The most stereotyped of these grooming patterns, a "syntactic chain," has a particularly stereotyped order that recurs thousands of times more often than could occur by chance. The purpose of the present study was to identify the crucial site within the striatopallidal system where lesions disrupt the syntax or serial order of syntactic grooming chains without disrupting constituent movements. Small excitotoxin lesions were made using quinolinic acid at bilateral sites within the dorsolateral, dorsomedial, ventrolateral, or ventromedial neostriatum, or in the ventral pallidum or globus pallidus of rats. An objective technique for mapping functional lesions was used to quantify cell death and to map precisely those lesions that disrupted grooming syntax. Our results identified a single site within the anterior dorsolateral neostriatum, slightly more than a cubic millimeter in size (1.3 x 1.0 x 1.0 mm), as crucial to grooming syntax. Damage to this site did not disrupt the ability to emit grooming actions. By contrast, damage to sites in the ventral pallidum and globus pallidus impaired grooming actions but left the sequential organization of grooming syntax intact. Neural circuits within this crucial "action syntax site" seem to implement sequential patterns of behavior as a specific function.

Immunological instability of persistent adenovirus vectors in the brain: peripheral exposure to vector leads to renewed inflammation, reduced gene expression, and demyelination

Nonreplicating adenovirus vectors are being developed as vehicles for the delivery of therapeutic genes in vivo. Whereas in many organs an antiviral T cell response eliminates the vector and damages local tissue, when adenovirus vectors are injected into the brain the subsequent immune attack can be ineffective, allowing the vector to persist. In the present study, E1-deleted human adenovirus vectors were injected into the caudate nucleus of rats. Two months later, expression of protein from the vector was still evident and little inflammation was seen. A subcutaneous injection of adenovirus vector at this time, however, led within 2 weeks to severe mononuclear inflammation and microglial activation in the caudate. This caused local demyelination and a decrease in detectable protein expression from the vector. Interestingly, intense microglial activation and numerous lymphocytes and monocytes were also seen in brain areas containing neurons capable of retrogradely transporting the adenovirus vector from the caudate. Control experiments established that this inflammation in distant brain areas was not a nonspecific consequence of degeneration. These experiments demonstrate that although adenovirus vectors can persist in the brain without causing chronic inflammation, they remain the potential target of a damaging cell-mediated immune response brought about by a subsequent peripheral exposure to vector. The finding of lymphocytes in brain areas that project to the caudate further shows that viral antigens that are retrogradely transported by neurons can also be the target of a T cell attack.

Correlation of vacuous chewing movements with morphological changes in rats following 1-year treatment with haloperidol

Long-term treatment with the typical antipsychotic drug, haloperidol, can lead to a sometimes irreversible motor disorder, tardive dyskinesia (TD). It has been hypothesized that increased release of glutamate due to prolonged neuroleptic drug treatment may result in an excitotoxic lesion in specific neuronal populations within the basal ganglia, leading to TD. We reported that treatment with haloperidol for 1 month results in an increase in the mean percentage of striatal asymmetric synapses containing a perforated postsynaptic density (PSD) and that these synapses are glutamatergic. Using quantitative immunocytochemistry, we found that depending on how long the animals had been off haloperidol following subchronic (30 d) treatment, there was either a decrease (1 day off) or increase (3-4 days off) in the density of glutamate immunolabeling within the presynaptic terminals of synapses with perforated PSDs. Using a rat model for TD, animals in the current study were treated for 1 year with haloperidol and spontaneous oral dyskinesias (i.e. vacuous chewing movements, VCMs) were recorded. In these long-term treated animals we wanted to determine if there was a correlation between glutamate function, as measured by changes in synapses with perforated PSDs and the density of nerve terminal glutamate immunoreactivity, and VCM behavior. In drug treated rats which demonstrated either a high or low rate of VCMs, there was a significant increase in the mean percentage of asymmetric synapses in the dorsolateral striatum with perforated PSDs in both haloperidol-treated groups compared to vehicle-treated rats. There was a small but significant increase in the density of glutamate immunolabeling within striatal nerve terminals of the high VCM group compared to the low VCM group. There was, however, no difference in the density of glutamate immunolabeling between the high VCM group compared to the vehicle-treated animals. One reason for this lack of difference was partially due to a significant increase in nerve terminal area within the high VCM group compared to either the low VCM- or vehicle-treated groups. The larger nerve terminal size in the high VCM group may be due to a small but sustained increase in glutamate neurotransmitter release with the ability of the terminal to maintain its supply of glutamate, while the terminals in the low VCM group showed evidence of glutamate depletion. This finding would be consistent with the hypothesis that increased glutamatergic activity may be associated with TD.

Cortical lesions induce an increase in cell number and PSA-NCAM expression in the subventricular zone of adult rats

The subventricular zone (SVZ) bordering the lateral ventricle is one of the few regions of adult brain that contains dividing cells. These cells can differentiate into neurons in vivo after migration into the olfactory bulb and in vitro in the presence of appropriate growth factors. Little is known, however, about the fate of these cells in vivo after brain injury in adults. We examined cell number and expression of differentiation markers in the SVZ of adult rats after cortical lesions. Aspiration lesions of the sensorimotor cortex in adult rats induced a transient doubling of the number of cells in the SVZ at the level of the striatum without consistent increases in bromodeoxyuridine-labeled cells. Immunoreactivity to the polysialylated neural cell adhesion molecule, expressed by the majority of cells of the SVZ during development, increased dramatically after lesion. In contrast, immunolabeling for molecules found in mature neurons and glia did not increase in the SVZ after lesion, and immunoreactivity for growth factors that induce differentiation of SVZ cells in vitro decreased or remained undetectable, suggesting that lack of appropriate growth factor expression may contribute to the lack of differentiation of the newly accumulated cells in vivo. The data reveal that cells of the SVZ are capable of plasticity in the adult rat after brain injury in vivo and that the newly accumulated cells retain characteristics seen during development.

Contrasting effects of chronic clozapine, Seroquel(TM) (ICI 204,636) and haloperidol administration of deltaFosB-like immunoreactivity in the rodent forebrain

We have recently demonstrated that specific neuroanatomical patterns of Fos-like immunoreactivity are predictive of atypical antipsychotic activity. However, the fact that neuroleptics must be administered chronically in order to generate both extrapyramidal side effects and an optimal therapeutic response calls into question the relevance of acute changes in Fos-like immunoreactivity for these slowly developing events. Fos-like immunoreactivity cannot be used to identify neurons activated by chronic neuroleptic administration because the increase in Fos-like immunoreactivity produced by an acute antipsychotic injection is dramatically reduced following repeated neuroleptic administration. In contrast, expression of the immediate-early gene product deltaFosB is persistently elevated in the striatum by chronic haloperidol administration. This suggests that deltaFosB-like immunoreactivity may be used to identify neurons activated by chronic antipsychotic administration. Since typical and atypical neuroleptics elevate Fos-like immunoreactivity in different regions of the forebrain acutely, the purpose of the present study was to determine whether typical (haloperidol) and atypical (clozapine, ICI 204,636) antipsychotics produce distinct patterns of elevated deltaFosB-like immunoreactivity in the forebrain after chronic administration. Administration of haloperidol (2 mg/kg/day) to rats for 19 days induced a homogeneous elevation of neurons which displayed deltaFosB-like immunoreactivity in the ventral, medial and dorsolateral aspects of the striatum. Chronic haloperidol administration did not enhance the deltaFos-like immunoreactivity in the prefrontal cortex and lateral septal nucleus. Repeated administration of clozapine (20 mg/kg/day) and ICI 204,636 (20 mg/kg/day) for 19 days elevated deltaFosB-like immunoreactivity not only in the ventral striatum but also in the prefrontal cortex and lateral septal nucleus. However, these compounds had weak effects on deltaFosB-like immunoreactivity in the dorsolateral striatum. These results suggest that a preferential action on limbic structures such as the prefrontal cortex, ventral striatum and lateral septal nucleus may account for the ability of chronic clozapine and ICI 204, 636 administration to reduce the symptoms of schizophrenia without generating extrapyramidal side effects.

Unilateral frontal cortex ablation producing neglect causes time-dependent changes in striatal glutamate receptors

This study's goal is to identify adaptations involving striatal glutamate (GLU) or dopamine (DA) receptors that may contribute to recovery of function following cortical injury. Unilateral aspiration of the medial agranular region of frontal cortex (AGm) in rats produces neglect of contralateral stimuli. Pharmacological and immunocytochemical studies suggest that glutamatergic and dopaminergic processes within striatum may contribute to spontaneous recovery from this neglect. This study examined by autoradiography radioligand binding to striatal GLU and DA receptor subfamilies in AGm-ablated rats surviving 5 days (unrecovered) or 3 or more weeks (recovered) postsurgery. Density of radioligand binding was quantified in striatal subregions by computerized image analysis. Compared to striatal binding densities in the intact hemisphere, [3H]kainate binding and [3H]GLU binding to NMDA receptors were decreased in the lesioned hemisphere of unrecovered AGm-ablated rats, but normalized (for kainate) or increased (for NMDA) in the lesioned hemisphere of recovered rats. Ablation of AGm did not affect [3H]AMPA binding or the binding of [3H]SCH23390, [3H]spiperone, or [3H]mazindol to dopaminergic D1 or D2 receptor subfamilies, or to DA uptake sites, respectively. The results suggest that a small percentage of NMDA and kainate receptors are located on corticostriatal axon terminals, and that over time an upregulation of striatal NMDA and/or kainate receptors may offset the loss of cortical glutamatergic input caused by cortical injury. These time-dependent alterations in GLU receptors may contribute to the recovery of function and normalizations of immediate early gene expression seen weeks after AGm ablation. Upregulation of striatal dopamine receptors was not evident, and thus is unlikely to mediate recovery from neglect produced by cortical injury.

Glutamate receptor agonist injections into the dorsal striatum cause contralateral turning in the rat: involvement of kainate and AMPA receptors

Unilateral stimulation of glutamate receptors in the dorsal striatum of intact rats resulted in contralateral turning. Turning behavior was recorded for 20 min following unilateral intrastriatal injections (0.5 microliter) in chronically cannulated rats. Kainate injections caused a dose-dependent increase in contralateral rotation that was blocked by the glutamate receptor antagonist 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX), the action potential blocker tetrodotoxin, and by increasing doses of the dopamine receptor antagonist cis-flupenthixol. Injections of alpha-amino-3-hydroxy-5-methylisoxazole-4-propionic acid (AMPA) also caused rotation that was blocked with co-injections of CNQX, tetrodotoxin or cis-flupenthixol. Neither CNQX nor tetrodotoxin injected alone caused turning. This effect is dopamine-dependent, and may result from a kainate or AMPA-induced increase in dopamine release. Glutamate receptor agonist injections into the striatum may cause contralateral turning by degrading information in ascending cortical projections and may further influence locomotion via basal ganglia output nuclei projections to the brainstem.

Frontal cortex ablation reversibly decreases striatal zif/268 and junB expression: temporal correspondence with sensory neglect and its spontaneous recovery

This study's goal is to identify subcortical adaptations that may contribute to recovery of function following cortical injury. After unilateral aspiration of the medial agranular region of frontal cortex (AGm), rats demonstrate neglect of contralateral stimuli and recover within 3-4 weeks. Previous studies indicate that compensatory neural alterations involving dopamine (DA) occur following this cortical injury and that recovery from neglect produced by frontal injury is accompanied by normalization of glucose utilization within subcortical structures including the basal ganglia. The current study examined Zif and JunB, IEG protein products constitutively expressed in striatum, rendering it possible to investigate the effects of unilateral AGm ablation on striatal function during unstimulated as well as amphetamine-stimulated conditions. Five days after surgery, when contralateral neglect was still evident, the numbers of Zif-like or Jun-like immunoreactive (IR) nuclei in the ipsilateral striata of AGm-ablated rats were reduced. These lesion effects were similar for both constitutive and amphetamine-stimulated IEG expression and were restricted to the dorsolateral caudate-putamen, where excitatory input from AGm is most dense. In contrast, 3 or more weeks after AGm ablation, in rats demonstrating recovery, normal striatal Zif- and JunB-like immunoreactivity occurred. Thus, striatal zif/268 and junB expression is reduced 5 days after AGm injury in rats demonstrating neglect and normalized 3 or more weeks later in recovered rats. These findings indicate that adaptations involving the striatal medium spiny neuron, a site of convergence of cortical glutamatergic and nigral dopaminergic afferents, may contribute to behavioral recovery following neocortical injury.